System and method for detecting and characterizing touch inputs at a human-computer interface

ABSTRACT

One variation of a method for detecting an input at a touch sensor—including a force-sensitive layer exhibiting variations in local resistance responsive to local variations in applied force on a touch sensor surface and a set of drive and sense electrodes—includes: driving a drive electrode with a drive signal; reading a sense signal from a sense electrode; detecting a alternating-current component and a direct-current component of the sense signal; in response to a magnitude of the direct-current component of the sense signal falling below a threshold magnitude, detecting an input on the touch sensor surface during the scan cycle based on the alternating-current component of the sense signal; and, in response to the magnitude of the direct-current component of the sense signal exceeding the threshold magnitude, detecting the input on the touch sensor surface during the scan cycle based on the direct-current component of the sense signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. patent application Ser. No.17/196,966, filed on 9 Mar. 2021, which claims the benefit of U.S.Provisional Patent Application No. 62/987,290, filed on 9 Mar. 2020,which is incorporated in its entirety by this reference.

This Application is related to U.S. patent application Ser. No.14/499,001, filed on 26 Sep. 2014, which is incorporated in its entiretyby this reference.

TECHNICAL FIELD

This invention relates generally to the field of systems and morespecifically to a new and useful human-computer interface system in thefield of systems.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B are flowchart representations of a method and a system;

FIG. 2 is a flowchart representation of one variation of the method andthe system;

FIG. 3 is a flowchart representation of one variation of the method;

FIG. 4 is a flowchart representation of one variation of the method;

FIGS. 5A and 5B are flowchart representations of one variation of themethod;

FIGS. 6A and 6B are flowchart representations of one variation of themethod; and

FIG. 7 is a schematic representation of one variation of the system.

DESCRIPTION OF THE EMBODIMENTS

The following description of embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Variations, configurations, implementations, example implementations,and examples described herein are optional and are not exclusive to thevariations, configurations, implementations, example implementations,and examples they describe. The invention described herein can includeany and all permutations of these variations, configurations,implementations, example implementations, and examples.

1. Method

As shown in FIGS. 1A, 1B, and 3 , a method S100 for detecting andcharacterizing touch inputs includes: detecting an input on a touchsensor surface 140 comprising a set of drive electrode and senseelectrode pairs and a conductive force-sensitive layer 130 in BlockS110, driving a drive electrode in a first drive electrode and senseelectrode pair to a reference potential in Block S120; sampling anoutput signal at a sense electrode in the first drive electrode andsense electrode pair in Block S130; calculating a capacitance valuebetween the drive electrode and the sense electrode based on an ACcomponent of the output signal in Block S140; calculating a resistancevalue between the drive electrode and the sense electrode based on a DCcomponent of the output signal in Block S150; and calculating a forcemagnitude and location of the input on the touch sensor surface 140based on the resistance value and the capacitance value in Block S160.

1.1 Applications

Generally, method S100 can be executed by a system 100 that includes: aset of drive electrode and sense electrode pairs (hereinafter a“pressure sensor array”) arranged across a substrate 110; a controller160; and a force-sensitive layer 130 exhibiting changes in contactresistance across adjacent drive and sense electrode pairs (or changesin local bulk resistance) as a function of local applied force, arrangedover the pressure sensor array, and forming an air gap 150 over thepressure sensor array; and a tactile surface over the force-sensitivelayer 130. The controller 160 can execute Blocks of the method S100 to:interpret changes in capacitance between drive electrode and senseelectrode pairs as local positions of light touches and/or initialcontact of heavy touches on the tactile surface, which displace theforce-sensitive layer 130 toward the pressure sensor array and thuslocally compress the air gap 150); and to interpret changes inresistance between drive electrode and sense electrode pairs as localpositions and force magnitudes of touches on the tactile surface.

More specifically, the force-sensitive layer 130 is arranged over thepressure sensor array to form a small (e.g., 5-micron-tall,10-micron-tall) air gap 150 between the pressure array and a proximalsurface of the force-sensitive layer 130. The force-sensitive layer 130exhibits a permittivity (e.g., dielectric constant) that differs fromthe permittivity of air, such that displacement of the force-sensitivelayer 130 toward the pressure sensor array results in a change inoverall permittivity between the drive electrode and sense electrodepairs, thereby effecting internal capacitive coupling between thesedrive electrode and sense electrode pairs as a function of (e.g.,proportional to) local changes in height of the air gap 150. In thisconfiguration, even very light forces (e.g., forces under 5 grams)applied over the tactile surface may displace the force-sensitive layer130 toward the pressure sensor array and significantly reduce the heightof the air gap 150, thus changing (e.g., increasing) internalcapacitance between a subset of drive electrode and sense electrodepairs adjacent this force. The system 100 can therefore sample (e.g.,measure, calculate) the internal capacitive coupling between each driveelectrode and sense electrode pair in the pressure sensor array during ascan cycle (and/or over a sequence of scan cycles) and detect,characterize, and track application of (very) light forces on thetactile surface based on derived changes in internal capacitive couplingbetween these drive electrode and sense electrode pairs.

Concurrently, the controller 160 can: detect changes in resistancebetween drive electrode and sense electrode pairs resulting fromapplication of larger forces—on the tactile surface—that compress theforce-sensitive layer 130 against the pressure sensor array and yieldlocal changes in bulk resistance of the force-sensitive layer 130 orchanges in contact resistance between the force-sensitive layer andadjacent drive and sense electrode pairs electrodes; and interpret thesechanges in resistance as location and magnitude of larger forces appliedto the tactile layer. The controller 160 can then merge locations andforce magnitudes of higher-force inputs (e.g., greater than 5 grams)derived from changes in resistance between drive electrode and senseelectrode pairs with locations of lower-force inputs (e.g., less than 5grams) derived from capacitive coupling between drive electrode andsense electrode pairs to generate more comprehensive representation ofinputs across the tactile surface during a scan cycle (e.g., a forcedistribution, a contact map).

In particular, the system 100 can set a minimum threshold change inresistance for detecting inputs on the touch sensor surface 140 based onresistance changes between drive electrode and sense electrode pairs inorder to reject noise and reduce false positive detection of inputs onthe tactile surface. However, the system 100 can also substitute theresistance-based dynamic range of the pressure sensor array below thisminimum threshold change in resistance with input detection based onchanges in internal capacitive coupling between the drive electrode andsense electrode pairs. More specifically, the system 100 is configuredto: drive a drive electrode in the pressure sensor array to a referencepotential (e.g., with an input waveform); measure an output signal(e.g., voltage, current draw) at a corresponding sense electrode over asampling period; and interpret (e.g., analyze, disambiguate) the outputsignal to concurrently derive (e.g., calculate) a capacitance valuebetween the drive electrode and sense electrode pair based oncharacteristics of the output signal. For example, the controller 160can derive the capacitance value proportional to an amplitude ofoscillation in the sense electrode output signal (e.g., an AC componentof the output signal). Concurrently and/or subsequently, the controller160 can calculate the resistance value proportional to a steady-statevalue of the sense electrode output signal (e.g., a DC component of theoutput signal). For very light input forces (e.g., less than 5 grams),the capacitive component of the sense electrode output signal dominates,thus enabling the system 100 to accurately detect an object at thelocation on the tactile surface corresponding to the drive electrode andsense electrode pair even if the drive electrode and sense electrodepair exhibits little to no change in resistive coupling.

Additionally, because the internal capacitance between drive electrodeand sense electrode pairs depends only on the geometry of the pressuresensor array and the size of the air gap 150, the system 100 canleverage sampled capacitance values in order to detect and characterizeinputs unaffected by certain defects in the system 100, such asdiscontinuities and/or irregularities (e.g., dead zones) in theforce-sensitive layer 130, print defects in the substrate 110, and/orresidual dust on the force-sensitive layer 130 or electrode surfaces.Similarly, because the conductive force-sensitive layer 130 confineselectric fields generated by drive electrodes below the tactile surface,the system 100 can detect contact between any type of object and thetactile surface (e.g., a gloved finger, a pen, a stylus), as well asdetect and characterize inputs in the presence of water and/or othermaterials on the touch sensor surface 140.

1.2 System

As shown in FIGS. 1A and 1B, the system 100 includes: a touch sensorsurface 140; a set of drive electrode and sense electrode pairs 120arranged across a substrate 110 (e.g., a rigid PCB); a controller 160coupled to the set of drive electrodes and sense electrodes; and aforce-sensitive layer 130 arranged between the touch sensor surface 140and the set of drive electrode and sense electrode pairs 120, includinga conductive material that exhibits variations in local bulk resistanceand/or local contact resistance responsive to forces applied over (e.g.,exerted on) the touch sensor surface 140. In one implementation, thesystem 100 includes a grid array of interdigitated drive electrodes andsense electrodes (or “array of drive electrode and sense electrodes”)patterned across (e.g., deposited on, integrated into) a rigidsubstrate, such as a fiberglass PCB or other PCB on a rigid backing. Theforce-sensitive layer 130 is arranged into a continuous layer (e.g.,arranged on a back side of the touch sensor surface 140, installed at asmall (e.g., 5-micron-tall, 10-micron-tall) separation over the array ofdrive electrode and sense electrode pairs 120, and connected to thesubstrate 110 about its perimeter, forming a thin air gap 150 betweenthe force-sensitive layer 130 and the sensor elements.

In this configuration, application of a localized force to the touchsensor surface 140 (e.g., a touch input) displaces and/or compresses theforce-sensitive layer 130, thereby changing the resistance across localdrive electrode and sense electrode pairs 120 proportional to themagnitude of the applied force. Additionally, forces applied over thetouch sensor surface 140 reduce the local separation between the(conductive) force-sensitive layer 130 and the array of drive electrodeand sense electrodes, thereby changing internal capacitive couplingsbetween adjacent drive electrode and sense electrode pairs 120. Thecontroller 160 is therefore configured to: drive a set of the driveelectrodes to a reference potential; sample corresponding output signals(e.g., voltages) at corresponding sense electrodes; and analyze (e.g.,interpret, disambiguate) the output signals to derive (e.g., compute,calculate) a capacitance value and a resistance value across each driveelectrode and sense electrode pair 120 within the system 100. Thecontroller 160 can then transform the resulting sets of resistancevalues and capacitance values into positions and/or magnitudes ofdiscrete force inputs applied over the touch sensor surface 140 (e.g., aforce distribution) and a capacitance (e.g., touch) image representingthe positions and sizes of objects contacting the touch sensor surface140.

The system 100 can be integrated into a laptop computer, a portableelectronic device (e.g., a tablet, a smartphone, a wearable device), aperipheral keyboard and/or trackpad, or any other electronic device inorder to detect and characterize touch inputs by a user. For example,the substrate 110 can be bonded to the chassis of a laptop computer suchthat the touch sensor surface 140 defines an opaque touchpad and/orkeyboard surface. In another example, the system 100 can be arrangedunder a display to form a pressure-sensitive touch screen for a tablet,smartphone, or smartwatch. However, these examples are merelyillustrative. The system 100 can also be integrated into any suitableelectronic device in order to detect and characterize inputs.

1.3 Internal Capacitance Between Drive Electrode and Sense Electrodes

As shown in FIG. 2 , the force-sensitive layer 130 can be arranged abovethe array of drive electrode and sense electrodes and connected (e.g.,bonded, affixed) to the substrate no along its edges, thereby enclosinga thin (e.g., 5- to 10-micron tall) air gap 150 between electrodes inthe array of drive electrode and sense electrodes and the proximalsurface of the force sensitive layer. When driven at a referencepotential (e.g., during a scan cycle), drive electrodes in each driveelectrode and sense electrode pair 120 generate an electric field thatcan propagate through the air gap 150 (e.g., a dielectric) to acorresponding sense electrode, resulting in an internal capacitivecoupling between the drive electrode and sense electrode pairs 120.However, the (conductive) force-sensitive layer 130 prevents propagationof electric field lines through the force-sensitive layer 130 andconfines the electric fields generated by drive electrodes to the airgap 150 between the array of drive electrode and sense electrodes andthe force-sensitive layer 130. Thus, displacement of the force-sensitivelayer 130 toward the array of drive electrode and sense electrodes(e.g., resulting from a force applied over the touch sensor surface 140)increases the electric flux permitted through the air gap 150 (e.g., ata constant reference potential) and/or the vertical dimensions of theintermediate dielectric (e.g., air), thereby increasing the internalcapacitance between drive electrode and sense electrode pairs 120adjacent an object or input on the touch sensor surface 140.

Generally, the small separation (e.g., less than 10 microns) between thearray of drive electrode and sense electrodes and the force-sensitivelayer 130 prevents electric fields emitted by a drive electrode in afirst drive electrode and sense electrode pair 120 from propagating tosense electrodes in other, nearby drive electrode and sense electrodepairs 120. Additionally, even under light forces (e.g., less than 5grams, 0.05 Newtons) applied over the touch sensor surface 140, theforce-sensitive layer 130 can experience displacements that aresignificant proportional to the z-height of the air gap 150. Thus, driveelectrode and sense electrode pairs 120 proximal an input area mayexperience relatively large changes in internal capacitive coupling withno changes in resistive coupling (e.g., in response to very lightapplications of force). Thus, the controller 160 can sequentially driveeach drive electrode in the array of drive electrode and senseelectrodes to a reference potential and extract capacitance valuesacross each drive electrode and sense electrode pair 120 from outputsignals received at corresponding sense electrodes in order to detectand track inputs (e.g., over a sequence of scan cycles) on the touchsensor surface 140 defining a large range of applied force.

1.4 Signal Processing and Input Characterization

As shown in FIG. 4 , Blocks of the method S100 recite: detecting aninput on a touch sensor surface 140 comprising a set of drive electrodeand sense electrode pairs 120 and a conductive force-sensitive layer 130in Block S110. Generally, the controller 160 is configured to: sample aset of resistance values across drive electrode and sense electrodepairs 120 in the system 100; compare the set of resistance values and/ora force magnitude calculated based on the set of resistance values to athreshold value; and detect application of an input (e.g., presence ofan object) and/or force in response to a resistance value or the forcemagnitude exceeding the threshold value. For example, during an initialscan cycle, the controller 160 can: sequentially drive each column ofdrive electrodes in the array of drive electrode and sense electrodes toa reference potential (e.g., while floating all other rows of driveelectrodes); sequentially sample steady-state (e.g., DC) voltages and/orcurrent draws at corresponding columns of sense electrodes; andtransform the voltages sampled at the columns of sense electrodes into aset of resistance values and/or the magnitude and location of a forceapplied over the touch sensor surface 140. The controller 160 can thencompare the set of resistance values and/or the force magnitude to apredetermined threshold value in order to detect application of an inputto the touch sensor surface 140. Therefore, in one implementation, thecontroller 160 can detect initial application of an input or contact onthe touch sensor surface 140 based on resistance values sampled duringan initial resistance scan cycle.

Blocks of the method S100 further recite: driving a drive electrode in afirst drive electrode and sense electrode pair 120 to a referencepotential in Block S120; and sampling an output signal at a senseelectrode in the first drive electrode and sense electrode pair 120 inBlock S130. Generally, the controller 160 is configured to, duringsubsequent scan cycles: drive a drive electrode with an input voltage(e.g., an input waveform); and sample a sequence of output values and/oran output waveform at a corresponding sense electrode over a samplingperiod. In particular, the controller 160 can output a fixed referencepotential (e.g., a square wave input) or a time-varying potential (e.g.,a sine wave input) to the drive electrode. In one implementation, thecontroller 160 can select (e.g., previously select, concurrently select)a sampling window for a set of ADCs within the controller 160 based oncharacteristics (e.g., amplitude, frequency) of the input waveform andthe geometry of the drive electrode and sense electrode pair 120. Thecontroller 160 can then sample the voltage at the sense electrode over asequence of sampling periods (e.g., 10 samples, 50 samples, 100 samples)and construct an output signal including time series of sense electrodevoltages and/or current draws corresponding to the drive potential. Inanother implementation, the controller 160 can continuously sample thevoltage and/or current draw from the sense electrode over a samplingperiod and construct an output signal defining a continuous waveform(e.g., a voltage curve, a current curve).

Blocks of the method S100 further recite: calculating a capacitancevalue between the drive electrode and the sense electrode based on an ACcomponent of the output signal in Block S140; and calculating aresistance value between the drive electrode and the sense electrodebased on a DC component of the output signal in Block S150. Generally,the controller 160 is configured to: analyze (e.g., interpret, decomposedisambiguate) a sense electrode output (e.g., a potential curve);measure (e.g., derive, determine, calculate) a capacitive couplingbetween a drive electrode and sense electrode pair 120 based on a firstcomponent of the output signal; and simultaneously and/or subsequentlymeasure (e.g., derive, determine, calculate) a resistive couplingbetween the drive electrode and sense electrode pair 120 based on asecond component of the output signal. More specifically, the controller160 can interpret the sense electrode output (e.g., a time series ofsense electrode voltages, a voltage curve) as a superposition of acapacitive signal component and a resistive signal component. Thecontroller 160 can then derive a capacitance value between the driveelectrode and sense electrode pair 120 based on characteristics of thecapacitive signal component and subsequently or concurrently derive aresistance value across the drive electrode and sense electrode pair 120based on characteristics of the resistive signal component.

In one implementation, the controller 160 can drive the drive electrodeto a fixed reference potential (e.g., a square wave input) to generate asense electrode output such as the output signal shown in FIG. 3 .Generally, the sense electrode output (e.g., voltage curve) is asuperposition of a damped AC signal (e.g., oscillating around a groundpotential) of an amplitude and/or frequency proportional to thecapacitance between the drive electrode and the sense electrode pair anda logistic potential curve (e.g., a DC resistive signal) with asteady-state value proportional to the resistance between the driveelectrode and the sense electrode pair. The controller 160 can thereforebe configured to: measure the amplitude of the AC signal component(e.g., by calculating a difference between a global maximum on thevoltage curve and the steady-state/DC potential); measure the frequencyof the AC signal component (e.g., by measuring a duration between localmaxima of the AC signal component); and transform the measured amplitudeand/or frequency of the AC signal component into a capacitance valuebetween the drive electrode and the sense electrode based on derivedcorrelations and/or calibration data. Similarly, the controller 160 canbe configured to sample a steady-state value of the output signal (e.g.,a DC signal component, steady-state voltage) and to transform the steadystate voltage into a resistance value between the drive electrode andsense electrode pair 120.

In another implementation, the controller 160 can drive the driveelectrode with an oscillating reference potential (e.g., a sine waveinput) to generate a sense signal. In particular, the sense signalgenerated by a sinusoidal drive signal is a superposition of an undampedAC oscillation (e.g., a resistive signal component) with an amplitudeproportional to the resistance between the drive electrode and the senseelectrode, and a second, damped AC oscillation (e.g., a capacitivesignal component) with an amplitude and/or frequency proportional to thecapacitance between the drive electrode and the sense electrode that isphase-shifted relative to the resistive signal component. Generally, thecontroller 160 can be configured to differentiate (e.g., disambiguate,parse) the resistive AC signal component from the capacitive AC signalcomponent based on a phase difference between the two AC signalcomponents relative to the phase of the drive signal and/or an amplitudeincrease between capacitive and resistive regions of the sense signal.In one variation, the controller 160 can: drive the drive electrode withan oscillating drive signal and record a first sense signal;subsequently drive the drive electrode to a fixed (e.g., static)reference potential and record a second sense signal; calculate aresistance value between the drive electrode and the sense electrodebased on the second sense signal; generate a capacitive output signal bysubtracting the second sense signal from the first sense signal; andcalculate a capacitance value between the drive electrode and the senseelectrode based on an amplitude, frequency, and/or phase of thecapacitive output signal relative to the oscillating drive signal.

However, these examples are merely illustrative. The controller 160 canalso be configured to drive a drive electrode with any suitabletime-dependent input signal and execute corresponding processes toderive (e.g., measure, calculate, compute) both an internal capacitanceand a resistance between a drive electrode and sense electrode pair 120from the same sense signal, thereby enabling the controller 160 tosimultaneously sample resistance and capacitance data across driveelectrode and sense electrode pairs 120 during a single scan cycle.

Blocks of the method S100 further recite: calculating a force magnitudeand a location of the input on the touch sensor touch sensor surface 140based on the resistance value and the capacitance value in Block S160.Generally, the controller 160 is configured to: transform a calculatedresistance value between a drive electrode and sense electrode pair 120into a magnitude and/or location of a force applied over the touchsensor surface 140 at the location of the drive electrode and senseelectrode pair 120; and interpret the calculated capacitance valuebetween the drive electrode and sense electrode pair 120 as a presenceof an object (e.g., an input) contacting the touch sensor surface 140 atthe location of the drive electrode and sense electrode pair 120. Thus,as shown in FIG. 4 , the controller 160 can sample a set of resistancevalues and a set capacitance values by sequentially executing BlocksS120, S130, S140, and S150 of the method S100 for each drive electrodeand sense electrode pair 120 in the array of drive electrode and senseelectrodes during a scan cycle. The controller 160 can then transformthe set of resistance into a pressure image (e.g., a resistance image, aforce image) representing a force distribution across the area of thetouch sensor surface 140 (e.g., corresponding to application of aninput) during the scan cycle. Additionally and/or alternatively, thecontroller 160 can transform the set of capacitance values into acapacitance image representing the locations and sizes of objectscontacting the touch sensor surface 140 during the scan cycle. Thecontroller 160 can then derive (e.g., determine, compute) a location ofan input on the touch sensor surface 140 and/or locations of multiplesimultaneous inputs (e.g., a multi-finger gesture) on the touch sensorsurface 140 based on the capacitance image. For example, the controller160 can calculate an (x,y) location of a centroid of a high capacitance(or low capacitance) region of the capacitance image and associate thecentroid's location with the location of an input on the touch sensorsurface 140. The controller 160 can therefore calculate (e.g.,determine) locations of inputs on the touch sensor surface 140 basedonly on measured changes in internal capacitances between driveelectrode and sense electrode pairs 120 in the array of drive electrodeand sense electrodes (e.g., independent of resistance data), therebyenabling the system 100 to accurately detect and track low-forcemagnitude (e.g., less than 5 grams, 0.05 Newtons) inputs one the touchsensor surface 140.

In one implementation, the controller 160 is further configured tocombine (e.g., integrate, overlay) the pressure image with thecapacitance image and output a touch image (e.g., an annotated touchimage) that includes the total force applied over the touch sensorsurface 140 and/or a force distribution across the touch sensor surface140, as well as locations, sizes and/or types of objects contacting thetouch sensor surface 140 during each scan cycle. Generally, thecontroller 160 is configured to sequentially execute scan cycles (e.g.,Blocks S120, S130, S140, S150, and S160 of method) at a predetermined orconfigurable scan frequency (e.g., 10 Hz, 50 Hz, 100 Hz) in order tocontinuously detect, characterize, and/or track movement of objects andforces on the touch sensor surface 140. Thus, when the system 100 isintegrated into an electronic device (e.g., a laptop computer, asmartphone), the device can then execute command functions based ontouch images output by the controller 160, such as updating the positionof a cursor.

1.5 Baselining and Redundancy

The controller 160 is further configured to modify a capacitance imagegenerated during a scan cycle based on pressure images (e.g., resistanceimages, force images) generated during the scan cycle or during previousscan cycles. Generally, the capacitance image may exhibit secondaryeffects produced by air movement within the gap between theforce-sensitive layer 130 and the pressure during or succeeding theapplication of a force to the touch sensor surface 140, which can reduceaccuracy of location calculations based on the capacitance image. Forexample, the capacitance image may include a trail corresponding tomovement of an input across the touch sensor surface 140, whichartificially displaces (e.g., shifts, pulls back) the centroid of theinput area. Therefore, in one implementation, the controller 160 candetermine an input area and/or input size on the touch sensor surface140 (e.g., areas of statistically significant, non-zero forceapplication) based on a pressure image generated in a previous scancycle and subtract out, ignore, or otherwise exclude capacitance valuesmeasured at drive electrode and sense electrode pairs 120 outside theinput area in order to reduce or eliminate artifacts in the capacitanceimage. For example, the controller 160 can register (e.g., determine,compute) a circular region of the capacitance image centered around alocal maximum in a corresponding force distribution (e.g., based on apressure image from a previous scan cycle) and subtract out (e.g.,baseline) capacitance values measured from drive electrode and senseelectrode pairs 120 outside the circular region (e.g., input area)during the current scan cycle and subsequent scan cycles. Thus, thecontroller 160 can exclude capacitance values measured from distal driveelectrode and sense electrode pairs 120 outside the input area in orderto eliminate ripples, trails and other secondary effects within the airgap 150 from the capacitance image, thereby increasing the accuracy oflocation calculations based on the capacitance image.

The controller 160 is further configured to continuously update theposition of the input area based on capacitance images generated duringsubsequent scan cycles. For example, the controller 160 can track afeature of the capacitance image associated with an input or an objecton the touch sensor surface 140 throughout a sequence of scan cycles.Thus, the controller 160 can detect and track (e.g., measure, record)movement of an input across the touch sensor surface 140 based oncapacitance images or differences in capacitance images generated over asequence of scan cycles (e.g., independent of corresponding resistancedata), enabling the system 100 to detect and track the location of verylight (e.g., less than 5 grams, 0.05 Newtons) applied forces.Additionally, the controller 160 can compare resistance values andcapacitance values from each drive electrode and sense electrode pair120 in the array of drive electrode and sense electrodes and/or comparea pressure image with a corresponding capacitance image in order toidentify and track inputs through any defective regions in the system100 (e.g., due to small discontinuities/dead zones in theforce-sensitive layer 130, print defects in the substrate 110 and/ordust or other micro-particles on the force-sensitive layer 130 orelectrode surfaces).

2. Variation

As shown in FIGS. 1A, 1B, 6A, and 6B, one variation of the methodS100—for detecting an input at a system 100 comprising a force-sensitivelayer 130 exhibiting variations contact resistance across adjacent driveand sense electrode pairs (or variations in local bulk resistance)responsive to local variations in applied force on a touch sensorsurface 140, a set of drive electrodes, and a set of senseelectrodes—includes: driving a first drive electrode, in the set ofdrive electrodes, with a drive signal during a first scan cycle in BlockS120; reading a first sense signal from a first sense electrode, in theset of sense electrodes and paired with the first drive electrode,during the first scan cycle in Block S130; detecting a firstalternating-current component of the first sense signal in Block S140;detecting a first direct-current component of the first sense signal inBlock S150; in response to a magnitude of the first direct-currentcomponent of the first sense signal falling below a threshold magnitude,detecting a first input on the touch sensor surface 140 during the firstscan cycle based on the first alternating-current component of the firstsense signal in Block S162; and, in response to the magnitude of thefirst direct-current component of the first sense signal exceeding thethreshold magnitude, detecting the first input on the touch sensorsurface 140 during the first scan cycle based on the firstdirect-current component of the first sense signal in Block S164.

One variation of the method S100 5A and 5B, includes, during a firstscan cycle: reading a first set of sense signals from a set of driveelectrode and sense electrode pairs 120 in Block S130, each sense signalin the first set of sense signals representing a resistance between adrive electrode and sense electrode pair 120, in the set of driveelectrode and sense electrode pairs 120, during the first scan cycle;and detecting a first input at a first location on a touch sensorsurface 140 during the first scan cycle in Block S164 based on a firstdirect-current component of a first sense signal, in the first set ofsense signals, indicating a first change in resistance between a firstdrive electrode and sense electrode pair 120, in the set of driveelectrode and sense electrode pairs 120, located proximal the firstlocation. This variation of the method S100 also includes, during asecond scan cycle succeeding the first scan cycle: reading a second setof sense signals from the set of drive electrode and sense electrodepairs 120 in Block S130; and tracking the first input from the firstlocation to a second location on the touch sensor surface 140 during thesecond scan cycle based on a second direct-current component of a secondsense signal, in the second set of sense signals, indicating a secondchange in resistance between a second drive electrode and senseelectrode pair 120, in the set of drive electrode and sense electrodepairs 120, located proximal the second location in Block S164. Thisvariation of the method S100 further includes, during a third scan cyclesucceeding the second scan cycle: reading a third set of sense signalsfrom the set of drive electrode and sense electrode pairs 120 in BlockS130; detecting a third direct-current component of a third sense signalread from a third drive electrode and sense electrode pair 120, in theset of drive electrode and sense electrode pairs 120, located proximal athird location on the touch sensor surface 140 in Block S150; detectinga third alternating-current component of the third sense signal in BlockS140; and, in response to a third magnitude of the third direct-currentcomponent falling below a threshold magnitude, tracking the first inputfrom the second location to the third location on the touch sensorsurface 140 during the third scan cycle based on a third amplitude ofthe third alternating-current component of the third sense signalindicating a third change in capacitance between the third driveelectrode and sense electrode pair 120 in Block S162.

2.1 Applications

Generally, in this variation, the system 100 can include: a substrateno; an array of drive electrode and sense electrode pairs 120 arrangedacross the substrate 110 (hereinafter the “sensor array”); aforce-sensitive layer 130 arranged over the array of drive electrode andsense electrode pairs 120 and containing a material (e.g., conductiveparticulate in a polymer binder) exhibiting local changes in contactresistance across adjacent drive and sense electrode pairs (or localchanges in local bulk resistance or impedance) as a function of appliedforce; and a touch sensor surface 140 over the force-sensitive layer130.

2.2 Drive Electrode and Sense Electrode Pair as Variable Resistor

The system 100 further includes a controller 160 that executes Blocks ofthe method S100 to: drive drive electrodes in the sensor array with adrive signal (e.g., to a reference voltage potential); read sensesignals (e.g., voltage timeseries) from sense electrodes in the sensorarray; extract direct-current (or “DC”) components from these sensesignals (e.g., steady-state voltages); and interpret force magnitudes ofinputs across the touch sensor surface 140 based on these DC sensesignal components during a scan cycle, as shown in FIGS. 1B, 5A, 5B, 6A,and 6B,

More specifically, the force-sensitive layer 130 bridges a gap between adrive electrode and sense electrode pair 120 and exhibits changes incontact resistance with the adjacent drive electrode and sense electrodepair 120 (or changes in local bulk resistance) as a function of forceapplied to the touch sensor surface 140 over this drive electrode andsense electrode pair 120. Thus, as this applied force increases, thecontact resistance (or the local bulk resistance) of the force-sensitivelayer 130 between this drive electrode and sense electrode pair 120decreases, thereby yielding a greater voltage at the sense electrodewhen the controller 160 drives the adjacent drive electrode to areference voltage potential. Therefore, the voltage at the senseelectrode read by the controller 160 during a scan cycle represents alocal contact resistance (or bulk resistance) of the force-sensitivelayer 130 adjacent the drive electrode and sense electrode pair 120,which represents a magnitude of a force applied to the touch sensorsurface 140 over the drive electrode and sense electrode pair 120.Accordingly, the controller 160 can: interpret a magnitude of forceapplied to the touch sensor surface 140 over the drive electrode andsense electrode pair 120 during a scan cycle based on the sense signal(e.g., a voltage) read from the sense electrode and known electricalcharacteristics of the force-sensitive layer 130; and detect an input onthe touch sensor surface 140 over the drive electrode and senseelectrode pair 120 based on this force, such as in response to thisforce exceeding a minimum contact force threshold (e.g., five grams, 0.5Newtons) that drives the force-sensitive layer 130 into contact with thedrive electrode and sense electrode pair 120. More specifically, a driveelectrode and sense electrode pair 120 and an adjacent region of theforce-sensitive layer 130 can form a variable-resistor that exhibits acharacteristic resistance as a function of applied force (when theforce-sensitive layer 130 is in contact with both the drive electrodesand sense electrodes) as shown in FIGS. 1A and 1B, and the controller160 can read a sense signal (e.g., a voltage, a resistance) from thevariable-resistor and interpret presence and force magnitude of an inputon the touch sensor surface 140 over the drive electrode and senseelectrode pair 120 based on this sense signal.

Furthermore, the controller 160 can concurrently execute this processfor all drive electrode and sense electrode pairs 120 in the sensorarray during one scan cycle to: interpret magnitudes of forces appliedacross the touch sensor surface 140 based on sense signals read fromeach sense electrode and known electrical characteristics of theforce-sensitive layer 130; detect inputs across the touch sensor surface140 based on these forces; and/or generate a touch image that representsa detected force at each drive electrode and sense electrode pair 120location and/or that specified lateral and longitudinal positions ofinputs on the touch sensor surface 140 and their detected forcemagnitudes.

2.3 Unintended Air Gap

In one application, assembly of the force-sensitive layer 130 over thesubstrate 110 produces regions of incomplete lamination between theforce-sensitive layer 130 and the substrate 110, thereby resulting involumes of air trapped between the force-sensitive layer 130 and thesubstrate 110 over a subset of drive electrode and sense electrode pairs120 in the sensor array, FIG. 1A. Similarly, particulate trapped betweenthe force-sensitive layer 130 and the substrate 110 during assemblyand/or a lifting edge of an electrode on the substrate 110 may preventcomplete lamination between the substrate 110 and the force-sensitivelayer 130 and thus produce similar volumes of air therebetween.

Each trapped volume of air may separate the force-sensitive layer 130from an adjacent drive electrode and sense electrode pair 120 such thatthe conductance between these drive electrode and sense electrode pairs120 is or approaches a null value (i.e., such that the resistance acrossthese drive electrode and sense electrode pairs 120 approaches aninfinite value). Furthermore, application of a force on the touch sensorsurface 140 over a trapped air volume may displace this air laterally,but the force-sensitive layer 130 may remain out of contact with thedrive electrode and sense electrode pair 120 until a larger force inexcess of the contact force threshold (e.g., greater than five grams,0.5 Newtons) is applied to the touch sensor surface 140 over the trappedair volume to drive the force-sensitive layer 130 into full contact withthe drive electrode and sense electrode pair 120. Because theforce-sensitive layer 130 remains out of contact with the driveelectrode and sense electrode pair 120 for inputs less than the contactforce threshold, the resistance across the drive electrode and senseelectrode pair 120 (and therefore the DC sense signal component read forthe sense electrode) may remain effectively unchanged over a range oflight to very-light inputs on the touch sensor surface 140 (e.g.,between 1 and 5 grams, 0.01 to 0.05 Newtons), thereby preventing thecontroller 160 from detecting both presence and force magnitude of suchlight to very-light inputs based solely on the resistance across thedrive electrode and sense electrode pair 120 (i.e., based solely on theDC components of sense signals read from the drive electrode and senseelectrode pair 120).

Furthermore, the controller 160 may otherwise interpret application of aforce equal to the contact force threshold over the drive electrode andsense electrode pair 120 as a baseline (or nominal, null) forcemagnitude. Accordingly, the controller 160 may fail to detect an inputof force magnitude less than the contact force threshold over thetrapped air volume given only the DC component of the sense signal readfrom the drive electrode and sense electrode pair 120. Upon detecting aninput over the trapped air volume, the controller 160 may also calculatea force magnitude of this input that is offset from—and less than—thetrue force magnitude of the input by the contact force threshold givenonly the DC component of the sense signal read from the drive electrodeand sense electrode pair 120.

2.3.1 Drive and Sense Electrode Pair as Variable Capacitor

However, a drive electrode and sense electrode pair 120 separated fromthe force-sensitive layer 130 may form a parallel-plate air-gapcapacitor in parallel with the variable resistor formed by the driveelectrode and sense electrode pair 120 and the force-sensitive layer130, as described above. More specifically and as shown in FIGS. 1A and1B, the drive electrode and sense electrode pair 120, theforce-sensitive layer 130, and the trapped air volume can cooperate toform: a variable capacitor that exhibits a characteristic capacitancethat changes as a function of distance that the force-sensitive layer130 is depressed over the trapped air volume (and therefore a forceapplied to the touch sensor surface 140 over the trapped air volume);and a variable resistor connected to the variable capacitance inparallel and that exhibits a characteristic resistance that changes as afunction of local force applied to the touch sensor surface 140.

The variable capacitance and the variable resistor can cooperate to forma high-pass filter that passes only high-frequency components of a drivesignal—input to the drive electrode during a scan cycle—to the sensesignal. In particular, when the controller 160 drives the driveelectrode with a drive signal (e.g., a single rising edge of a squarewave up to a reference voltage potential) during a scan cycle, theair-gap capacitor formed by the drive electrode and sense electrode pair120 can pass higher-frequency components of this drive signal to thesense electrode, which produces an oscillating voltage component at thesense electrode. When an input is applied to the touch sensor surface140 over the drive electrode and sense electrode pair 120, the trappedair volume is displaced laterally as the force-sensitive layer 130 movestoward the drive electrode and sense electrode pair 120, thereby:reducing the height of the air gap 150 between the drive electrode andsense electrode pair 120; increasing the characteristic capacitance ofthe air-gap capacitor; passing more of the high-frequency components ofthe drive signal to the sense electrode; and increasing the amplitude ofthe oscillating voltage component of the sense signal read from thesense electrode. Therefore, depression of the touch sensor surface 140over a trapped air volume may: reduce the height of the trapped airvolume; decrease the air gap 150 between this drive electrode and senseelectrode pair 120; increase the capacitance of the air-gap capacitorformed by this drive electrode and sense electrode pair 120; and pass agreater amplitude of high-frequency components of the drive signal tothe sense electrode, which result in a larger-amplitude AC component inthe sense signal read from the sense electrode during a scan cycle.

2.3.2 DC and AC Sense Signal Components

Furthermore, because a drive electrode and sense electrode pair 120, anadjacent region of the force-sensitive layer 130, and an air volumetrapped therebetween cooperate to form a variable resistor and avariable capacitor connected in parallel, the drive electrode and senseelectrode pair 120 can pass both DC and AC components of the drivesignal—input to the drive electrode during a scan cycle—to the senseelectrode, which yields a sense signal that contains both DC and ACcomponents, as shown in FIGS. 1A, 1B, and 3 . However, the variableresistor passes DC components of the drive signal exclusively, and thevariable capacitor passes AC components of the drive signal exclusively.Therefore, the controller 160 can disambiguate components of the senseelectrode directly passed by the variable resistor and the variablecapacitor based on the DC and AC components of the sense signal,respectively.

2.3.3 Input and Applied Force Detection

Accordingly, the controller 160 can: extract a DC component from thesense electrode (e.g., a DC voltages); calculate a magnitude of the DCsense signal component (which represents a resistance across theadjacent region of the force-sensitive layer 130); interpret a firstresistance-based force value applied over the drive electrode and senseelectrode pair 120 based on the magnitude of the DC sense signalcomponent; extract the AC component from the sense electrode; calculatean amplitude (e.g., a peak-to-peak amplitude) of the AC sense signalcomponent (which represents a capacitance across the drive electrode andsense electrode pair 120); and interpret a second capacitance-basedforce value applied over the drive electrode and sense electrode pair120 based on the amplitude of the AC sense signal component, as shown inFIGS. 1A, 1B, 6A, and 6B.

For example, if the first resistance-based force value is null (e.g., ifthe magnitude of the DC sense signal component is approximately null),the controller 160 can estimate a total force applied to the touchsensor surface 140 over the drive electrode and sense electrode pair 120based on (e.g., equal to) the second capacitance-based force value—thatis, based on the amplitude of the AC components of the sense signal. Ifthe second capacitance-based force value—and therefore the amplitude ofthe AC components of the sense signal—exceeds a threshold, thecontroller 160 can thus: detect presence and force magnitude of an inputon the touch sensor surface 140 over the drive electrode and senseelectrode pair 120 based on (e.g., equal to) the secondcapacitance-based force value; and output the location and forcemagnitude of this input accordingly.

Similarly, if the first resistance-based force value exceeds a low forcethreshold (e.g., 10 grams, 0.1 Newtons), the controller 160 can estimatethe total force applied to the touch sensor surface 140 over the driveelectrode and sense electrode pair 120 based on (e.g., equal to) thefirst resolution-based force value and ignore the secondcapacitance-based force value because the force-sensitive layer 130 islikely to be in proper contact with the drive electrode and senseelectrode pairs 120 given this total applied force. If the firstresistance-based force value—and therefore the magnitude of the DCcomponent of the sense signal—exceeds a threshold, the controller 160can thus: detect presence and force magnitude of an input on the touchsensor surface 140 over the drive electrode and sense electrode pair 120based on (e.g., equal to) the first resistance-based force value; andoutput the location and force magnitude of this input accordingly.

However, if the first resistance-based force value is non-zero but lessthan the low force threshold (e.g., 10 grams, 0.1 Newtons), thecontroller 160 can estimate the total force applied to the touch sensorsurface 140 over the drive electrode and sense electrode pair 120 basedon a combination (e.g., an average, a sum) of the first resolution-basedforce value and the second capacitance-based force value (e.g., becausethe force-sensitive layer 130 may not yet be in proper contact with thedrive electrode and sense electrode pairs 120 and inconsistent contactbetween the force-sensitive layer 130 and the drive electrode and senseelectrode pair 120 may create induce noise in the sense signal).Accordingly, the controller 160 can: detect presence and force magnitudeof an input on the touch sensor surface 140 over the drive electrode andsense electrode pair 120 based on (e.g., based on a combination of) thefirst resistance-based force value and the second capacitance-basedforce value; and output the location and force magnitude of this inputaccordingly.

2.3.4 Force-Sensitive Layer as Electrical Shield

Furthermore, because the force-sensitive layer 130 contains conductivematerial, the force-sensitive layer 130 may also electrically shieldthese air-gap capacitors from electrical noise over the touch sensorsurface 140, thereby maintaining a high signal-to-noise ratio in the ACcomponent of this sense signal.

2.3.5 Entire Sensor

The controller 160 can execute the foregoing process to: derive DC andAC components from sense signals read from all drive electrode and senseelectrode pairs 120 during a scan cycle; interpret resistance-based andcapacitance-based force magnitudes of inputs applied over these driveelectrode and sense electrode pairs 120 during the scan cycle based onthe DC and AC components derived from their corresponding sense signal;and assemble these data to predict locations and force magnitudes ofinputs across the entire touch sensor surface 140.

For example, the controller 160 can execute Blocks of the method S100to: read sense signals from drive electrode and sense electrode pairs120 in the sensor array during a scan cycle; extract DC components fromthe sense signals; identify a first subset of DC sense signal componentsthat fall within a range of values that indicate proper local contactbetween the force-sensitive layer 130 and corresponding drive electrodeand sense electrode pairs 120 (e.g., voltages between 1% to 100% of thereference voltage potential of a drive signal); and identify a secondsubset of DC sense signal components that fall outside of this range ofvalues and therefore indicate presence of a trapped air volume betweenthe force-sensitive layer 130 and corresponding drive electrode andsense electrode pairs 120. Based on the first subset of DC sense signalcomponents, the controller 160 can then: identify a first subset ofdrive electrode and sense electrode pairs 120 in contact with theforce-sensitive layer 130 during the scan cycle; and then interpretforce magnitudes applied to the touch sensor surface 140 over this firstsubset of drive electrode and sense electrode pairs 120 (e.g., based onresistances represented in DC components of sense signals read fromthese drive electrode and sense electrode pairs 120 during the scancycle).

Conversely, the controller 160 can identify a second subset of driveelectrode and sense electrode pairs 120 that are not in contact with theforce-sensitive layer 130 during the scan cycle based on the secondsubset of AC sense signal components. Accordingly, the controller 160can: derive AC components from this second subset of sense signals; anddetect (light) forces applied to the touch sensor surface 140 over thesedrive electrode and sense electrode pairs 120 based on the magnitudes ofAC sense signal components read from these drive electrode and senseelectrode pairs 120 during the scan cycle.

Therefore, the controller 160 can execute Blocks of the method S100 to:detect presence and force magnitudes of inputs applied to the touchsensor surface 140 over a first subset of drive electrode and senseelectrode pairs 120 in proper contact with the force-sensitive layer 130based on DC components of sense signals read from these drive electrodeand sense electrode pairs 120; and detect presence and force magnitudesof inputs (e.g., low-force inputs) applied to the touch sensor surface140 over a second subset of drive electrode and sense electrode pairs120 not in contact with the force-sensitive layer 130 (e.g., due tomanufacturing defects) based on AC components of sense signals read fromthese drive electrode and sense electrode pairs 120.

2.3.6 Input Tracking

Furthermore, the controller 160 can execute Blocks of the method S100 totrack an input moving across the touch sensor surface 140 betweenregions that do and do not contain defects (e.g., trapped air volumes)based on AC sense signal components and DC sense signal components,respectively, in order to: preserve detection of a continuous input; andavoid premature interpretation of removal of the input from the touchsensor surface 140, such as especially for light-force inputs on thetouch sensor surface 140.

2.3.6.1 First Scan Cycle

In one implementation as shown in FIGS. 5A and 5B, during a first scancycle, the controller 160 can: serially drive the set of driveelectrodes with a drive signal in Block S120; and serially read sensesignals from each sense electrode in Block S130. For example, thecontroller 160 can: drive a drive electrode with a single rising edge ofa square wave up to a reference voltage potential; concurrently read atimeseries of voltages (i.e., a sense signal) from a corresponding senseelectrode over a time duration greater than multiple time constants ofan air-gap capacitor formed by this drive electrode and sense electrodepair 120 (e.g., five microseconds); and repeat this process for eachsense electrode in the sensor array. The controller 160 can then: derivea DC component (e.g., a steady-state voltage) from the sense signal readfrom each drive electrode and sense electrode pair 120 during the firstscan cycle in Block S150; generate a first DC image (or a “resistanceimage”) that contains an array of pixels representing magnitudes of DCcomponents of sense signals read from each sense electrode during thisfirst scan cycle in Block S150; and scan this first DC image for DCmagnitudes that indicate application of non-zero forces on the touchsensor surface 140.

For example, the controller 160 can: retrieve a baseline DC image thatrepresents baseline DC voltages of sense electrodes (or baselineresistances across drive electrode and sense electrode pairs 120) whenno input is applied to the touch sensor surface 140; subtract thebaseline DC image from the first DC image for the current scan cycle inorder to generate a first normalized DC image; transform normalized DCcomponent values in each pixel in the first normalized DC image into aforce value based on a force function (e.g., a scalar value or anonlinear model); generate a first DC force image that contains an arrayof pixels that represent forces carried by each corresponding driveelectrode and sense electrode pair 120 during this first scan cycle; andimplement a smoothing filter to reduce noise in the first DC forceimage.

The controller 160 can then: identify a first cluster of pixelsindicating non-zero (i.e., elevated) forces in the first DC force imagein Block S164; calculate a first location of a first input on the touchsensor surface 140 during the first scan cycle based on a centroid ofthis cluster of pixels; and interpret a total force magnitude of thisfirst input during the first scan cycle based on a combination (e.g., asum) of the individual force magnitudes represented by pixels in thiscluster of pixels in the first DC force image.

2.3.6.2 Second Scan Cycle

The controller 160 can: repeat this process during a second scan cycleto generate a second DC force image in Block S150; and scan a subregionof the second DC image—encompassing a location of the first inputdetected during the first scan cycle—for a second cluster of DC pixelscontaining non-zero force values. In response to detecting this secondcluster of DC pixels in the second DC force image, the controller 160can: implement input tracking techniques to link the second cluster ofDC pixels to the first input; calculate a second location of the firstinput on the touch sensor surface 140 during the second scan cycle basedon a centroid of this second cluster of DC pixels; and interpret a totalforce magnitude of this first input during the second scan cycle basedon a combination of the individual force magnitudes represented bypixels in this second cluster of DC pixels in the second DC force image.

2.3.6.3 Input Lost in Second DC Force Image

However, in response to absence of the second cluster of DC pixelsproximal the first location of the first input in the second DC forceimage (or in the second normalized DC image), the controller 160 can:derive an AC component from the sense signal read from each driveelectrode and sense electrode pair 120 during the second scan cycle inBlock S140; and generate a second AC image (or a “capacitance image”)that contains an array of pixels representing amplitudes of ACcomponents of sense signals read from each sense electrode during thissecond scan cycle in Block S140. The controller 160 can then scan asubregion of the second AC image—encompassing a location of the firstinput detected during the first scan cycle—for a second cluster of ACpixels containing non-zero AC amplitudes.

In response to detecting this second cluster of AC pixels in the secondAC image in Block S162, the controller 160 can: implement input trackingtechniques to link the second cluster of AC pixels to the first input;and calculate a second location of the first input on the touch sensorsurface 140 during the second scan cycle based on a centroid of thissecond cluster of AC pixels. The controller 160 can thus preservedetection of this first input as the first input moves: from the firstlocation on the touch sensor surface 140 over a first cluster of driveelectrode and sense electrode pairs 120 not separated from theforce-sensitive layer 130 by a defect (e.g., a trapped air volume) andthat present viable DC signals responsive to applied forces; to a secondlocation on the touch sensor surface 140 over a second cluster of driveelectrode and sense electrode pairs 120 that are separated from theforce-sensitive layer 130 by a defect and that do not present viable DCsignals responsive to applied forces (of limited force magnitude).

The controller 160 can also estimate the force magnitude of the firstinput over the second location based on the combined AC amplitudesrepresented in the second cluster of pixels in the second AC image. (Thecontroller 160 can additionally or alternatively convert the second ACimage to a second AC force image based on a capacitance-based forcefunction, such as by multiplying the second AC image by a scalar valueor passing AC magnitudes in the second AC image through a nonlinearforce model. The controller 160 can then implement the foregoing processbased on the second AC force image rather than the second AC image.)

2.3.6.4 Third Scan Cycle

Furthermore, the controller 160 can repeat this process during a nextscan cycle to: generate a third DC force image based on DC sense signalcomponents read from the sense electrodes in Block S150; scan asubregion of the third DC image—encompassing a location of the firstinput detected during the second scan cycle—for a second cluster of DCpixels containing non-zero force values; and implement input trackingtechniques to link this third cluster of DC pixels to the first input inBlock S164 if the third cluster of DC pixels is present in the third DCforce image. Similarly, if the third cluster of DC pixels is not presentin the third DC force image, the controller 160 can: generate and scan athird AC image for a third cluster of AC pixels containing non-zero ACamplitudes in Block S140; preserve detection of the first input inresponse to detecting this third cluster of AC pixels in the third ACimage proximal the last detected location of the first input in BlockS162; or end the first input in response to absence of such as clusterof AC pixels in the third AC image, as described below.

The controller 160 can therefore link the first input at the secondlocation to a third location on the touch sensor surface 140 based oneither DC or AC sense signal components captured during the third scancycle in order to continuously track the first input moving across thetouch sensor surface 140—such as approaching, moving over, and thenmoving past a defect (e.g., a trapped air volume) between theforce-sensitive layer 130 and the substrate 110 proximal the secondlocation.

2.3.6.5 Input Absent in Second AC Force Image

However, in response to detecting both absence of the second cluster ofDC pixels in the second DC force image and absence of the second clusterof AC pixels in the second AC image that indicate present of an input onthe touch sensor surface 140 proximal the last detected location of thefirst input, the controller 160 can: confirm that the first input wasremoved (or “released”) from the touch sensor surface 140; and end (or“close”) the first input accordingly in Block S170.

Additionally or alternatively, the controller 160 can repeat thisprocess over multiple subsequent scan cycles to scan DC and AC imagesfor indicators of the first input near its last detected location andonly end the first input in response to absence of such indicators inboth DC and AC images over multiple (e.g., two, five) consecutive scancycles.

2.3.6.6 DC/AC Sense Signal Component Transition

Therefore, by transitioning between DC and AC sense signal components todetect and track the first input—after initially detecting the firstinput via DC sense signal components—the controller 160 can: preventpremature loss of an input moving across the touch sensor surface 140(e.g., a “gesture”); track the complete path of the first input (and theforce magnitude of the first input along this path); and only end (or“close”) the first input when both the DC and AC sense signal componentsread from the sensor array both indicate absence of an applied forcenear the last detected location of the first input, as shown in FIGS. 5Aand 5B.

In this implementation, the controller 160 can also execute this processto concurrently track multiple discrete inputs on the touch sensorsurface 140 over multiple scan cycles and to

2.3.7 Defect Detection

In the foregoing implementation, during operation, the controller 160can execute the foregoing process to: detect the first input at thefirst location on the touch sensor surface 140 based on force valuescontained in a first cluster of DC pixels in a first DC force image;interpret a first force magnitude of the first input at the firstlocation based on force magnitudes represented in the first cluster ofDC pixels; detect absence of representation of the first input at andnear the first location in the later, second DC force image; and thengenerate and scan a second AC image for AC amplitudes that indicatepresence of an input near the first location responsive to absence ofrepresentation of the first input in the second DC force image.

Then, in response to detecting the first input in the second AC image atsecond location near the first location, the controller 160 can:preserve detection of the first input from the first location during thefirst scan cycle to the second location during the second scan cycle;and estimate a second force magnitude of the first input at the secondlocation based on amplitudes of AC pixels representing the first in thesecond AC image, as described above. The controller 160 can also flagthe second location as a location of a possible defect within the system100, such as if the second force magnitude derived from these AC sensesignal components is large or similar to the first force magnitude ofthe input at the first location, as shown in FIG. 5B.

2.3.7.1 Defect Map

Furthermore, the computer system 100 can then repeat the methods andtechniques described above for subsequent scan cycles to detect andtrack the first input. If the controller 160 can then tracks the firstinput to a third location based on a later, third DC force image—ratherthan a later, third AC image—the controller 160 can predict or confirmthe defect at the second location and annotate a defect map for thesystem 100 to indicate the defect at the second location.

Then, during future scan cycles, the controller 160 can: generate ACsub-images based on AC components of sense signals read from driveelectrode and sense electrode pairs 120 at (and around) the secondlocation indicated in the defect map; and scan these sub-images for ACamplitudes that indicate forces applied to the touch sensor surface 140at the second location, such as rather than or in addition to scanningcorresponding regions of DC force images for inputs. Therefore, becausethe defect at the second location may inhibit contact between theforce-sensitive layer 130 and drive electrode and sense electrode pairs120 at and near the second location, the controller 160 can detect andactivate an input at the second location on the touch sensor surface 140based on AC amplitudes contained in AC sub-images representing theregion around the second location rather than based on DC sense signalcomponents represented in DC force images.

Furthermore, the sizes, frequency, and distribution of such trapped airvolumes may vary and may be unpredictable across many units of thesystem 100. Therefore, upon detecting an input at the second locationbased on AC sense signal components read from the adjacent driveelectrode and sense electrode pairs 120 at a later time, the controller160 can also scan the concurrent DC force image for DC sense signalcomponents that also indicate this input at the second location. Then,upon detecting this input in the DC force image, the controller 160 canclear the defect at the second location from the defect map and revertto first scanning DC force images for inputs proximal the secondlocation.

The controller 160 can therefore repeat this process over time todevelop and maintain an accurate map of defects between theforce-sensitive layer 130 and the substrate no and can selectivelytransition between detecting initial application of inputs on the touchsensor surface 140 based on DC or AC sense signal components accordingto defects indicated in this defect map.

2.3.8 Dynamic Range Expansion

In another example, the controller 160 can also transition from a)detecting and tracking an input on the touch sensor surface 140 over atrapped air volume in Block S162 based on an AC sense signal componentread from a drive electrode and sense electrode pair 120 during a firstscan cycle to b) detecting and tracking this input at the same locationon the touch sensor surface 140 in Block S164 based on a DC sense signalcomponent read from this drive electrode and sense electrode pair 120during a later scan cycle in response to the force magnitude of thisinput increasing sufficiently to drive the touch sensor surface 140 intocontact with the adjacent drive electrode and sense electrode pairs 120,which produces a non-zero DC sense signal component at the driveelectrode and sense electrode pair 120.

In a similar example, the controller 160 can transition from a)detecting and tracking an input on the touch sensor surface 140 in BlockS164 based on a DC sense signal component read from a drive electrodeand sense electrode pair 120 during a first scan cycle to b) detectingand tracking this input at this same location based on an AC sensesignal component read from this drive electrode and sense electrode pair120 during a later scan cycle in Block S162 in response to the forcemagnitude of this input decreasing sufficiently to enable theforce-sensitive layer 130 to separate from the drive electrode and senseelectrode pairs 120, thereby yielding a (near-) zero DC sense signalcomponent at the sense electrode.

Therefore, by executing Blocks of the method S100, the controller 160can detect and track inputs over a large range of force magnitudes overthe entire touch sensor surface 140, including: low-force inputs (e.g.,less than 10 grams or 0.1 Newtons) over trapped air volumes based on ACsense signal components; very-low-force inputs (less than 5 grams or0.05 Newtons) over regions of the force-sensitive layer 130 in contactwith the substrate no based on combinations of DC and AC sense signalcomponents; higher-force inputs (e.g., greater than 10 grams or 0.1Newtons) that displace trapped air volumes to bring the force-sensitivelayer 130 into contact with adjacent drive electrode and sense electrodepairs 120 based on DC sense signal components; and higher-force (e.g.,greater than 5 grams or 0.05 Newtons) inputs that compress theforce-sensitive layer 130 against drive electrode and sense electrodepairs 120—over regions of the substrate no excluding voids ormanufacturing defects—based on DC sense signal components.

2.3.9 Sensor Scope

Furthermore, the sizes, frequency, and distribution of such trapped airvolumes may vary and may be unpredictable across many units of thesystem 100. Application of an input on the touch sensor surface 140and/or a gesture applied across the touch sensor surface 140 mayredistribute (or “move”) a trapped air volume across the substrate 110in unpredictable ways. Therefore, the controller 160 can execute Blocksof the method S100 to automatically transition between to detectinginputs across the touch sensor surface 140 based on DC and AC sensesignal components read from the sensor array in order to compensate forchanges in sizes, frequency, and/or distribution of trapped air volumesbetween the substrate 110 and the force-sensitive layer 130 over time.

2.4 Intended Air Gap

In one variation as shown in FIGS. 6A and 6B, the system 100 isassembled with an intended air gap 150 between the force-sensitive layer130 and the substrate 110. For example, during assembly of the system100, a volume of air (or gas, such as nitrogen argon) sufficient to forma uniform air gap 150 10 microns in height is injected between theforce-sensitive layer 130 and the substrate 110. In another example, theforce-sensitive layer 130 is selectively adhered or bonded to thesubstrate 110 around drive electrode and sense electrode pairs 120 toform an open-cell or closed-cell network of air gaps 150 aroundindividual drive electrode and sense electrode pairs 120 or clusters ofdrive electrode and sense electrode pairs 120.

Thus, in this variation, the controller 160 can execute Blocks of themethod S100: to detect very-light inputs (e.g., inputs of forcemagnitude less than 5 grams or 0.05 Newtons) on the touch sensor surface140 based on AC sense signal components that represent changes incapacitance between drive electrode and sense electrode pairs 120resulting from changes in height of the adjacent air gap 150 (e.g., from10 microns to 1 micron); and to detect heavier inputs (e.g., inputs offorce magnitude greater than 10 grams or 0.1 Newtons) on the touchsensor surface 140 based on DC sense signals that represent changes inresistance between drive electrode and sense electrode pairs 120resulting from compression of the adjacent region of the force-sensitivelayer 130, as shown in FIG. 6B. In this variation, the controller 160can also execute Blocks of the method S100 to detect light inputs (e.g.,inputs of force magnitude between 5 and 10 grams or between 0.05 and 0.1Newtons) based on a combination (e.g., a sum, an average) of both AC andDC sense signal components read from sense electrode, as shown in FIG.6B.

For example, the controller 160 can implement methods and techniquesdescribed above to: drive the array of drive electrodes with the drivesignal during a scan cycle in Block S120; and read timeseries sensesignals from the array of sense electrodes during this scan cycle inBlock S130.

The controller 160 can then: extract DC signal components from eachsense signal; calculate a magnitude of each DC component (e.g., amagnitude from 0 Volts to a peak voltage); and represent each DCmagnitude in a corresponding pixel in a DC image for this scan cycle inBlock S150. The controller 160 can also: subtract a stored baseline DCimage from this DC image to generate a normalized DC image; or convertthe DC image into a DC force image by applying a resistance force model(e.g., a scalar value) to the DC image and then substrate a baseline DCforce image from this DC force image to generate a normalized DC forceimage.

Concurrently, the controller 160 can: extract AC signal components fromeach sense signal; calculate an amplitude (e.g., a peak-to-peak voltage)of each AC component; and represent each AC amplitude in a correspondingpixel in an AC image for this scan cycle in Block S140. The controller160 can also: subtract a baseline AC image from this AC image togenerate a normalized AC image; or convert the AC image into an AC forceimage by applying a capacitance force model (e.g., a scalar value) tothe AC image and then subtract a baseline AC force image to generate anormalized AC force image.

The controller 160 can then scan the DC image (or the normalized DCimage, the DC force image) for clusters of DC magnitudes that indicateinputs on the touch sensor surface 140. For each input thus detected inthe DC image, the controller 160 can derive a first totalresistance-based force of the input based on individual force magnitudesrepresented in the corresponding cluster of pixels in the DC image.

Similarly, the controller 160 can scan the AC image (or the normalizedAC image, the AC force image) for clusters of AC amplitudes thatindicate inputs on the touch sensor surface 140. For each input thusdetected in the AC image, the controller 160 can derive a second totalcapacitance-based force of the input based on individual forcemagnitudes represented in the corresponding cluster of pixels in the ACimage.

The controller 160 can then link cospatial DC- and AC-based inputsdetected from these DC and AC sense signal components during this scancycle.

Then, for each detected input associated with a first totalresistance-based force exceeding a high resistance-based force threshold(e.g., 10 grams, 0.1 Newtons), the controller 160 can label the inputwith its corresponding first total resistance-based force in Block S164.

Similarly, for each detected input associated with a first totalresistance-based force between the high resistance-based force thresholdand a low resistance-based force threshold (e.g., 5 grams, 0.05Newtons), the controller 160 can: calculate a combination (e.g., a sum,an average, a weighted average) of its corresponding first totalresistance-based force and second total capacitance-based force; andlabel the input with this force combination in Block S160.

Furthermore, for each input associated with a non-zero second totalcapacitance-based force and a first total resistance-based force lessthan the low resistance-based force threshold (e.g., between 0 and 5grams, between 0 and 0.05 Newtons), the controller 160 can label theinput with its corresponding second total capacitance-based force inBlock S1562.

The controller 160 can then compile the locations and force magnitudesof these inputs into a force image for the current scan cycle and outputthis force image to a connected or integrated computing device (e.g., alaptop computer, a desktop computer), which may then manipulate agraphical user interface with gestures, cursor movements, and/or clicksrepresented in this force image. The controller 160 can then repeatthese processes for each subsequent scan cycle.

Therefore, the controller 160 can execute Blocks of the method S100 tofuse DC and AC sense signal components—representing resistance andcapacitance characteristics of the drive electrode and sense electrodepairs 120 in the sensor array—to detect both a) low- tohigh-force-magnitude inputs on the touch sensor surface 140 b) and low-to very-low-force-magnitude inputs on the touch sensor surface 140,respectively. Accordingly, the controller 160 can achieve a wide dynamicrange for detection of both presence and force magnitude of inputs onthe touch sensor surface 140 during operation.

Furthermore, in the foregoing implementation, the controller 160 canimplement similar methods and techniques to detect presence and forcemagnitudes of inputs over individual drive electrode and sense electrodepairs 120 in the sensor array based on values contained in individual DCand AC pixels in the DC and AC images, respectively, rather than detectpresence and force magnitudes indicate greater areas of inputs appliedto the touch sensor surface 140 based on clusters of DC and AC pixels inthe DC and AC images.

2.5 Sensor Array System

Therefore, as described above and shown in FIGS. 1A and 1B, the system100 can include: a substrate 110; an array of drive electrode and senseelectrode pairs 120 arranged on the substrate 110; a force-sensitivelayer 130 coupled to the substrate 110, abutting the array of driveelectrode and sense electrode pairs 120, and exhibiting variations inlocal contact (or bulk resistance) responsive to variations in appliedforce; and a touch sensor surface 140 arranged over the substrate 110.The system 100 can further include a controller 160 configured to,during a first scan cycle: read a first sense signal from a first driveelectrode and sense electrode pair 120, in the array of drive electrodeand sense electrode pairs 120; detect a first alternating-currentcomponent of the first sense signal; detect a first direct-currentcomponent of the first sense signal; and, in response to a firstmagnitude of the first direct-current component of the first sensesignal falling below a threshold magnitude, detect a first input on thetouch sensor surface 140 at a first location proximal the first driveelectrode and sense electrode pair 120 based on the firstalternating-current component of the first sense signal. The controller160 can be further configured to, during a second scan cycle: read asecond sense signal from a second drive electrode and sense electrodepair 120, in the array of drive electrode and sense electrode pairs 120;detect a second direct-current component of the second sense signal;and, in response to the second magnitude of the second direct-currentcomponent of the second sense signal exceeding the threshold magnitude,detect a second input on the touch sensor surface 140 at a secondlocation proximal the second drive electrode and sense electrode pair120 based on the second direct-current component of the second sensesignal.

In this implementation: the array of drive electrode and sense electrodepairs 120 can be arranged over a top layer of the substrate 110; theforce-sensitive layer 130 can be arranged over the substrate no andinclude a first region that entraps a volume of air over the first driveelectrode and sense electrode pair 120; the first drive electrode andsense electrode pair 120 and a first region of the force-sensitive layer130 adjacent the first drive electrode and sense electrode pair 120 cancooperate to form a first variable resistor that passes direct-currentcomponents of a drive signal, input to a first drive electrode, to afirst sense electrode in the first drive electrode and sense electrodepair 120; and the first drive electrode and sense electrode pair 120 andthe volume of air can cooperate to form a first variable air-gapcapacitor connected in parallel to the first variable resistor and thatpasses high-frequency components of the drive signal to the first senseelectrode.

Furthermore, in this implementation, a first region of theforce-sensitive layer 130 can: entrap the volume of air of a nominalheight over the first drive electrode and sense electrode pair 120 in anominal state during absence of inputs on the touch sensor surface 140;and displace the volume of air laterally across the substrate 110 andmoves toward the first drive electrode and sense electrode pair 120 toincrease characteristic capacitance of the variable air-gap capacitorresponsive to application of the first input on the touch sensor surface140 at the first location proximal the first drive electrode and senseelectrode pair 120. Accordingly, the controller 160 can interpret afirst force magnitude of the first input on the touch sensor surface 140during the first scan cycle proportional to a first amplitude of thefirst alternating-current component of the first sense signal.

(The controller 160 can also read a third sense signal from the firstdrive electrode and sense electrode pair 120 and detect a thirddirect-current component of the third sense signal. Then, in response toa third magnitude of the third direct-current component of the thirdsense signal exceeding the threshold magnitude, the controller 160 can:detect a third input on the touch sensor surface 140 at the firstlocation proximal the first drive electrode and sense electrode pair120; calculate a third change in resistance across the first driveelectrode and sense electrode pair 120 during the third scan cycle basedon the third magnitude of the third direct-current component of thesecond sense signal; and interpret a third force magnitude of the thirdinput on the touch sensor surface 140 during the third scan cycleproportional to the third change in resistance across the first driveelectrode and sense electrode pair 120.)

Additionally or alternatively, the first region of the force-sensitivelayer 130 can: entrap the volume of air of a nominal height ofapproximately 10 microns over the first drive electrode and senseelectrode pair 120 in a nominal state during absence of inputs on thetouch sensor surface 140; include a conductive material thatelectrically shields the first drive electrode and sense electrode pair120 from electrical noise above the touch sensor surface 140; anddisplace air laterally across the substrate 110 and moves toward thefirst drive electrode and sense electrode pair 120 to increasecapacitance of the first drive electrode and sense electrode pair 120responsive to application of the first input on the touch sensor surface140 at the first location proximal the first drive electrode and senseelectrode pair 120. Accordingly, the controller 160 can: interpret areduction in height of the volume of air, from the nominal height,during the first scan cycle proportional to the amplitude of the firstalternating-current component of the first sense signal; retrieve aspring model representing combined spring constants of theforce-sensitive layer 130 and the volume of air moving laterally betweenthe force-sensitive layer 130 and the substrate no; and interpret afirst force magnitude of the first input on the touch sensor based onthe reduction in height of the volume of air and the spring constant.

2.6 Discrete Array of Drive Electrode and Sense Electrodes

In one variation as shown in FIG. 7 , the system 100 includes acontroller 160 and an array of discrete (e.g., discontinuous) pressuresensor elements arranged beneath the touch sensor surface 140, eachincluding: a drive electrode and sense electrode pair 120 (e.g., a pairof interdigitated electrodes) formed on a substrate no (e.g., a commonPCB that spans the array of discrete pressure sensors); aforce-sensitive layer 130 arranged over the drive electrode and senseelectrode pair 120; a deflection spacer (e.g., a silicone pad) or aspring that couples the discrete pressure sensor and the substrate no toa chassis of an electronic device.

In one implementation, in this variation: the substrate no can define a3.5-inch by 4.5-inch area; the touch sensor surface 140 can be arrangedover a top layer of the substrate 110 to form 3.5-inch by 4.5-inchactive input area; each pressure sensor can include a 0.25-inch-diameterforce-sensitive layer 130 coupled to a drive electrode and senseelectrode pair 120 spanning 0.25-inch-diameter region on a bottom layerof the substrate 110; and the system 100 can include ten pressuresensors supporting the perimeter of the substrate 110 on the chassis ofthe computing device.

In one example of this implementation, the force-sensitive layer 130 canbe bonded to the substrate 110 at each pressure sensor location withintended contact between the force-sensitive layer 130 and the driveelectrode and sense electrode pair 120 under a no-load condition on thetouch sensor surface 140. However, in this example, a defect in theforce-sensitive layer 130, a defect in the substrate 110, or depressionof the touch sensor surface 140 remotely from this pressure sensor maycreate an air gap 150 between or otherwise separate from the driveelectrode and sense electrode pair 120 from the force-sensitive layer130 in this pressure sensor. Therefore, in this example, the controller160 can implement methods and techniques described above to detect andcharacterize a force carried by the pressure sensor based on ACcomponents of a sense signal read from the pressure sensor given absenceof a DC sense signal component in this sense signal.

In another example of this implementation, the force-sensitive layer 130in a pressure sensor is bonded (e.g., affixed) to the substrate 110about its perimeter and around the adjacent drive electrode and senseelectrode pair 120 to seal a volume of air—inside the pressuresensor—that forms an air gap 150 of a target height (e.g., 10 microns)between the force-sensitive layer 130 and the drive electrode and senseelectrode pair 120 under a no-load condition on the touch sensor surface140. In this example, the controller 160 can implement methods andtechniques described above to detect and characterize: a) low to highforce magnitudes (e.g., 10-250 grams, 0.1 to 2.5 Newtons) carried by thepressure sensor based on DC sense signal components read from the driveelectrode and sense electrode pair 120; very-low force magnitudes (e.g.,less than 5 grams, less than 0.05 Newtons) carried by the pressuresensor based on AC sense signal components read from the drive electrodeand sense electrode pair 120; and very-low to low force magnitudes(e.g., between 5 and 10 grams, between 0.05 and 0.1 Newtons) carried bythe pressure sensor based on combinations of DC and AC sense signalcomponents read from the drive electrode and sense electrode pair 120.

The systems and methods described herein can be embodied and/orimplemented at least in part as a machine configured to receive acomputer-readable medium storing computer-readable instructions. Theinstructions can be executed by computer-executable componentsintegrated with the application, applet, host, server, network, website,communication service, communication interface,hardware/firmware/software elements of a user computer or mobile device,wristband, smartphone, or any suitable combination thereof. Othersystems and methods of the embodiment can be embodied and/or implementedat least in part as a machine configured to receive a computer-readablemedium storing computer-readable instructions. The instructions can beexecuted by computer-executable components integrated bycomputer-executable components integrated with apparatuses and networksof the type described above. The computer-readable medium can be storedon any suitable computer readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component can bea processor but any suitable dedicated hardware device can(alternatively or additionally) execute the instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

We claim:
 1. A method for detecting an input at a touch sensorcomprising: during a first scan cycle: driving a first drive electrodewith a drive signal; reading a first sense signal from a first senseelectrode paired with the first drive electrode; detecting a firstalternating component of the first sense signal; detecting a firstdirect component of the first sense signal; and in response to a firstmagnitude of the first direct component of the first sense signalfalling below a threshold magnitude, detecting a first input on a touchsensor surface based on the first alternating component of the firstsense signal; and during a second scan cycle: driving the first driveelectrode with the drive signal; reading a second sense signal from thefirst sense electrode; detecting a second alternating component of thesecond sense signal; detecting a second direct component of the secondsense signal; and in response to a second magnitude of the second directcomponent of the second sense signal exceeding the threshold magnitude,detecting a second input on the touch sensor surface based on the seconddirect component of the second sense signal.
 2. The method of claim 1:wherein detecting the first direct component of the first sense signalcomprises detecting the first direct component of the first sense signalrepresenting a direct-current component of the drive signal passed by avariable resistor formed by the first drive electrode, the first senseelectrode, and a force-sensitive layer; and wherein detecting the firstalternating component of the first sense signal comprises detecting thefirst alternating component of the first sense signal representinghigh-frequency components of the drive signal passed by a variableair-gap capacitor: formed by the first drive electrode, the first senseelectrode, and a volume of air trapped between the force-sensitive layerand a substrate supporting the first drive electrode and the first senseelectrode; connected in parallel to the variable resistor; andelectrically shielded from the first input on the touch sensor surfaceby the force-sensitive layer.
 3. The method of claim 1, whereindetecting the first input on the touch sensor surface based on the firstalternating component of the first sense signal comprises: interpretinga force magnitude of the first input on the touch sensor surfaceproportional to a first amplitude of the first alternating component;and detecting the first input on the touch sensor surface in response tothe force magnitude exceeding a threshold force magnitude.
 4. The methodof claim 3, wherein interpreting the force magnitude of the first inputon the touch sensor comprises: interpreting a reduction in height of anair gap, between a force-sensitive layer and a substrate supporting thefirst drive electrode and the first sense electrode, proportional to thefirst amplitude of the first alternating component; retrieving a springconstant of the force-sensitive layer and the air gap; and interpretingthe force magnitude of the first input on the touch sensor based on thereduction in height of the air gap and the spring constant.
 5. Themethod of claim 1, wherein detecting the second input on the touchsensor surface based on the second direct component of the second sensesignal comprises: calculating a resistance across the first driveelectrode and the first sense electrode based on the second magnitude ofthe second direct component of the second sense signal; and interpretinga force magnitude of the second input on the touch sensor surfaceproportional to a difference between the resistance and a baselineresistance between the first drive electrode and the first senseelectrode.
 6. The method of claim 1: further comprising, during thefirst scan cycle, calculating a resistance across the first driveelectrode and the first sense electrode based on the first magnitude ofthe first direct component of the first sense signal; wherein detectingthe first input on the touch sensor surface based on the first directcomponent of the first sense signal comprises, in response to theresistance exceeding a high threshold resistance: interpreting a firstforce magnitude of the first input on the touch sensor surfaceproportional to a first amplitude of the first alternating component ofthe first sense signal; and detecting the first input, of the firstforce magnitude, on the touch sensor surface; wherein detecting thefirst input on the touch sensor surface based on the first alternatingcomponent of the first sense signal comprises, in response to theresistance falling below a low threshold resistance: interpreting asecond force magnitude of the first input on the touch sensor surfaceproportional to a difference between the resistance and a baselineresistance between the first drive electrode and the first senseelectrode; and detecting the first input, of the second force magnitude,on the touch sensor surface; and further comprising, during the firstscan cycle, in response to the resistance falling below the highthreshold resistance and exceeding the low threshold resistance:calculating a composite force magnitude based on a combination of thefirst force magnitude and the second force magnitude; and detecting thefirst input, of the composite force magnitude, on the touch sensor. 7.The method of claim 1: wherein driving the first drive electrode withthe drive signal during the first scan cycle comprises sequentiallydriving a set of drive channels, defining a set of drive electrodeswithin a sensor array, with the drive signal during the first scancycle; wherein reading the first sense signal from the first senseelectrode comprises sequentially reading a set of sense signals from aset of sense channels, defining a set of sense electrodes within thesensor array, during the first scan cycle; wherein detecting the firstinput on the touch sensor surface comprises detecting the first input ata first location on the touch sensor surface during the first scan cyclebased on the first sense signal, the first location proximal the firstdrive electrode and the first sense electrode; and further comprising,during the first scan cycle: detecting a third alternating component ofa third sense signal, in the set of sense signals, read from a thirdsense electrode in the set of sense electrodes; detecting a third directcomponent of the third sense signal; detecting absence of a third inputat a third location on the touch sensor surface in response to a thirdamplitude of the third alternating component falling below a thresholdamplitude and in response to a third magnitude of the third directcomponent falling below the threshold magnitude, the third locationproximal the third drive electrode and the third sense electrode; andcompiling the first location of the first input and absence of the thirdinput at the third location into a first touch image representing inputson the touch sensor surface.
 8. The method of claim 1: wherein detectingthe first input on the touch sensor surface comprises detecting thefirst input at a first location on the touch sensor surface during thefirst scan cycle based on the first sense signal, the first locationproximal the first drive electrode and the first sense electrode; andfurther comprising, during a third scan cycle: driving the first driveelectrode with the drive signal; reading a third sense signal from thefirst sense electrode; detecting a third alternating component of thethird sense signal; detecting a third direct component of the thirdsense signal; and detecting absence of the first input at the firstlocation on the touch sensor surface during the third scan cycle inresponse to a third amplitude of the third alternating component fallingbelow a threshold amplitude and in response to a third magnitude of thethird direct component falling below the threshold magnitude.
 9. Asystem comprising: a substrate: an array of drive electrode and senseelectrode pairs arranged on the substrate; a touch sensor surfacearranged over the substrate; and a controller configured to: during afirst scan cycle: read a first sense signal from a first drive electrodeand sense electrode pair, in the array of drive electrode and senseelectrode pairs; detect a first alternating component of the first sensesignal; detect a first direct component of the first sense signal; andin response to a first magnitude of the first direct component of thefirst sense signal falling below a threshold magnitude, detect a firstinput on the touch sensor surface at a first location proximal the firstdrive electrode and sense electrode pair based on the firstalternating-current component of the first sense signal; and during asecond scan cycle: read a second sense signal from a second driveelectrode and sense electrode pair, in the array of drive electrode andsense electrode pairs; detect a second direct component of the secondsense signal; and in response to the second magnitude of the seconddirect component of the second sense signal exceeding the thresholdmagnitude, detect a second input on the touch sensor surface at a secondlocation proximal the second drive electrode and sense electrode pairbased on the second direct-current component of the second sense signal.10. The system of claim 9, further comprising, a force-sensitive layercoupled to the substrate, abutting the array of drive electrode andsense electrode pairs, and exhibiting variations in local resistanceresponsive to variations in applied force.
 11. The system of claim 9:further comprising a force-sensitive layer arranged over the substrateand comprising a first region that entraps a volume of air over thefirst drive electrode and sense electrode pair; wherein the array ofdrive electrode and sense electrode pairs is arranged over a top layerof the substrate; wherein the first drive electrode and sense electrodepair and a first region of the force-sensitive layer adjacent the firstdrive electrode and sense electrode pair cooperate to form a firstvariable resistor that passes direct-current components of a drivesignal, input to a first drive electrode, to a first sense electrode inthe first drive electrode and sense electrode pair; and wherein thefirst drive electrode and sense electrode pair and the volume of aircooperate to form a first variable air-gap capacitor connected inparallel to the first variable resistor and that passes high-frequencycomponents of the drive signal to the first sense electrode.
 12. Thesystem of claim 11: wherein the first region of the force-sensitivelayer: entraps the volume of air of a nominal height of approximately 10microns over the first drive electrode and sense electrode pair in anominal state during absence of inputs on the touch sensor surface;comprises a conductive material that electrically shields the firstdrive electrode and sense electrode pair from electrical noise above thetouch sensor surface; and displaces air laterally across the substrateand moves toward the first drive electrode and sense electrode pair toincrease capacitance of the first drive electrode and sense electrodepair responsive to application of the first input on the touch sensorsurface at the first location proximal the first drive electrode andsense electrode pair; and wherein the controller is configured to:interpret a reduction in height of the volume of air, from the nominalheight, during the first scan cycle proportional to the amplitude of thefirst alternating component of the first sense signal; retrieve a springmodel representing combined spring constants of the force-sensitivelayer and the volume of air moving laterally between the force-sensitivelayer and the substrate; and interpret a first force magnitude of thefirst input on the touch sensor based on the reduction in height of thevolume of air and the spring constant.
 13. The system of claim 11:wherein the first region of the force-sensitive layer: entraps thevolume of air of a nominal height over the first drive electrode andsense electrode pair in a nominal state during absence of inputs on thetouch sensor surface; and displaces the volume of air laterally acrossthe substrate and moves toward the first drive electrode and senseelectrode pair to increase characteristic capacitance of the variableair-gap capacitor responsive to application of the first input on thetouch sensor surface at the first location proximal the first driveelectrode and sense electrode pair; and wherein the controller isconfigured to interpret a first force magnitude of the first input onthe touch sensor surface during the first scan cycle proportional to afirst amplitude of the first alternating-current component of the firstsense signal.
 14. The system of claim 13, wherein the controller isfurther configured to, during a third scan cycle: read a third sensesignal from the first drive electrode and sense electrode pair; detect athird direct component of the third sense signal; and in response to athird magnitude of the third direct component of the third sense signalexceeding the threshold magnitude: detect a third input on the touchsensor surface at the first location proximal the first drive electrodeand sense electrode pair; calculate a third change in resistance acrossthe first drive electrode and sense electrode pair during the third scancycle based on the third magnitude of the third direct component of thesecond sense signal; and interpret a third force magnitude of the thirdinput on the touch sensor surface during the third scan cycleproportional to the third change in resistance across the first driveelectrode and sense electrode pair.
 15. A method comprising: during afirst scan cycle: reading a first set of sense signals from a set ofdrive electrode and sense electrode pairs; and detecting a first inputat a first location on a touch sensor surface during the first scancycle based on a first direct component of a first sense signal, in thefirst set of sense signals, indicating a first change in electricalvalues between a first drive electrode and sense electrode pair, in theset of drive electrode and sense electrode pairs, located proximal thefirst location; during a second scan cycle succeeding the first scancycle: reading a second set of sense signals from the set of driveelectrode and sense electrode pairs; and tracking the first input fromthe first location to a second location on the touch sensor surfaceduring the second scan cycle based on a second direct component of asecond sense signal, in the second set of sense signals, indicating asecond change in electrical values between a second drive electrode andsense electrode pair, in the set of drive electrode and sense electrodepairs, located proximal the second location; and during a third scancycle succeeding the second scan cycle: reading a third set of sensesignals from the set of drive electrode and sense electrode pairs;detecting a third direct component of a third sense signal read from athird drive electrode and sense electrode pair, in the set of driveelectrode and sense electrode pairs, located proximal a third locationon the touch sensor surface; detecting a third alternating component ofthe third sense signal; and in response to a third magnitude of thethird direct component falling below a threshold magnitude, tracking thefirst input from the second location to the third location on the touchsensor surface during the third scan cycle based on the thirdalternating component of the third sense signal.
 16. The method of claim15, further comprising, during the third scan cycle, detecting releaseof the first input from the touch sensor surface in response to a thirdamplitude of the third alternating component of the third sense signalfalling below a threshold amplitude.
 17. The method of claim 15, furthercomprising, during a fourth scan cycle succeeding the third scan cycle:reading a fourth set of sense signals from the set of drive electrodeand sense electrode pairs; and tracking the first input from the thirdlocation to a fourth location on the touch sensor surface during thefourth scan cycle based on a fourth direct component of a fourth sensesignal, in the fourth set of sense signals, indicating a fourth changein electrical values between a fourth drive electrode and senseelectrode pair, in the set of drive electrode and sense electrode pairs,located proximal the fourth location.
 18. The method of claim 15,further comprising: during the third scan cycle, driving driveelectrodes, in the set of drive electrode and sense electrode pairs,with a drive signal; extracting, from the third sense signal, the thirddirect component of the third sense signal that represents adirect-current component of the drive signal passed by a variableresistor during the third scan cycle, the variable resistor formed bythe third drive electrode and sense electrode pair and an adjacentregion of a force-sensitive layer; and extracting, from the third sensesignal, the third alternating component of the third sense signalrepresenting high-frequency components of the drive signal passed by avariable air-gap capacitor during the third scan cycle, the variableair-gap capacitor: formed by the third drive electrode and senseelectrode pair and a volume of air trapped between the force-sensitivelayer and a substrate supporting the set of drive electrode and senseelectrode pairs; connected in parallel to the third variable resistor;and electrically shielded from the first input on the touch sensorsurface by the force-sensitive layer.
 19. The method of claim 15,further comprising: during the first scan cycle: calculating a firstresistance across the first drive electrode and sense electrode pairbased on a magnitude of the first direct component of the first sensesignal; interpreting a first force magnitude of the first input on thetouch sensor surface proportional to a difference between the firstresistance and a baseline resistance between the first drive electrodeand sense electrode pair; and outputting the first location and thefirst force magnitude of the first input; and during the third scancycle: interpreting a third force magnitude of the first input on thetouch sensor surface proportional to a third amplitude of the thirdalternating component of the third sense signal; and outputting thethird location and the third force magnitude of the first input.
 20. Themethod of claim 19: wherein calculating the first resistance across thefirst drive electrode and sense electrode pair comprises calculating alocal contact resistance of a first region of a force-sensitive layer,arranged over the first drive electrode and sense electrode pair, basedon the magnitude of the first direct component of the first sensesignal, the force-sensitive layer exhibiting variations in local contactresistance responsive to local variations in applied force on the touchsensor surface; and wherein interpreting the third force magnitude ofthe first input comprises: interpreting a third reduction in height ofan air gap, between the force-sensitive layer and a substrate supportingthe third drive electrode and sense electrode pair, proportional to thethird amplitude of the third alternating-current component of the thirdsense signal; retrieving a spring constant of the force-sensitive layerand the air gap; and interpreting the third force magnitude of the firstinput on the touch sensor during the third scan cycle based on the thirdreduction in height of the air gap and the spring constant.